1. Field of the Invention
The present invention relates to a reflection type liquid crystal display device in which a switching device and a reflector are formed on a semiconductor substrate, and a liquid crystal is sealed between the semiconductor substrate and a canmo electrode, a module for use in the reflection type liquid crystal display device, and a method of manufacturing the same.
2. Description of the Prior Art
As a head mount display and a projection type display, a reflection type liquid crystal display device which is called a silicon chip-based liquid crystal has recently been paid attention to.
FIG. 1 is a schematic view showing a principle of a reflection type liquid crystal display device using the silicon chip-based liquid crystal, and FIG. 2 is an assembly view showing a constitution of the same reflection type liquid crystal display device.
The reflection type liquid crystal display device is constituted of a light source 51 composed of red-, green-, and blue-color light emitting diodes; a polarizer 52; an analyzer 53; and a liquid crystal on silicon (hereinafter referred to as a LCOS) unit 54.
The LCOS unit 54 is constituted of a plurality of miniaturized reflectors (electrode) 61 arranged in a matrix fashion; a silicon chip module 54a in which devices such as CMOSs (not shown) are formed; and a liquid crystal panel 54b located on the silicon chip module 54a. Furthermore, the liquid crystal panel 54b is composed of a sealing member 66; a glass substrate 67; and a liquid crystal layer 68 sealed therebetween. A common electrode 67a made of a transparent electrically- conductive material is formed on a lower surface of the glass substrate 67.
FIG. 3 is a schematic plan view of the silicon chip module 54a. As shown in FIG. 3, a number of miniaturized reflectors 61 formed of aluminum alloy are arranged in the silicon chip module 54a in a matrix fashion. A MOS transistor (switching device) 62 is formed in each of the reflectors 61. Gate electrodes of the MOS transistors 62 arranged in the lateral direction are connected to the same gate bus line 73b, and the drains of the MOS transistors 62 arranged in the longitudinal direction are connected to the same data bus line 76b. Furthermore, the source of each MOS transistor 62 is connected to corresponding one of the reflectors 61.
FIG. 4 is a section view of the silicon chip module 54a. A MOS transistor constituted of a gate electrode 73a, a source 72a and a drain 72b is formed on a silicon substrate 71. Note that the gate bus line 73b shown in FIG. 3 is formed in the same wiring layer as that of the gate electrode 73a. 
An interlayer insulating film 74 is formed on the silicon substrate 71, and an intermediate wiring 76a and the data bus line 76b are formed on this interlayer insulating film 74. A plurality of connecting plugs 75a are buried in the interlayer insulating film 74, and the intermediate wiring 76a is connected to the source 72a of the MOS transistor via the connecting plugs 75a. The data bus line 76b is connected to the drain 72b of the MOS transistor.
An interlayer insulating film 77 is formed on the intermediate wiring 76a and the data bus line 76b. Moreover, the reflectors 61 are formed on the interlayer insulating film 77. A plurality of connecting plugs 78a are buried in the interlayer insulating film 77, and the reflector 61 is electrically connected to the source 72a of the MOS transistor via the connecting plug 78a, the intermediate wiring 76a and the connecting plug 75a. 
In the reflection type liquid crystal display device constituted in the above described manner, a beam of light emitted from the light source 51 is made to be uniform in its oscillation direction when the beam of light passes through the polarizer 52, as shown in FIG. 1. The polarized light that has passed through the polarizer 52 travels through the liquid crystal panel 54b of the LCOS unit 54, and reaches the reflector 61. The reflected light by the reflector 61 passes through the liquid crystal panel 54b again, and then tends to the analyzer 53. For example, in the case where the liquid crystal panel 54b is a TN (Twisted Nematic) mode, the oscillation direction of the light is twisted by a fixed angle while the light travels from the reflector 61 to the liquid crystal panel 54b in a state where no voltage is applied between the reflector 61 and the common electrode 67a. On the other hand, when a sufficiently high voltage is applied between the reflector 61 and the common electrode 67a, the oscillation direction of the light hardly change while the light travels from the reflector 61 to the liquid crystal panel 54b. For this reason, when the polarizer 52 and the analyzer 53 are disposed so that the light is shield with no application of a voltage, the light comes to transmit therethrough with an application of the voltage. By controlling the application voltage for each reflector 61, a desired image is displayed.
Incidentally, in the case of the reflection type liquid crystal display device having the above-described structure, it is important that a surface of the reflector 61 is flat. Therefore, before the reflector 61 is formed, a surface of the interlayer insulating film 77 is polished to be flat by use of, for example, a CNP (Chemical Mechanical Polishing) before the reflector 61 is formed.
However, the inventors of this application of the present invention consider that there are the problems described below in the foregoing conventional reflection type liquid crystal display device. To be specific, the surface of the silicon chip module 54a has irregularities equivalent to a thickness of the reflector 61. Therefore, if air enters gaps between the reflectors 61, a dielectric constant varies, and this causes a poor color tone and the like. In order to prevent such drawback, it is conceived that after the reflector is formed, an insulating material is buried in gaps between the reflectors by use of a method to coat SOG (Spin On Glass), to deposit a plasma oxide film or the like. However, the insulating substance such as SOG is attached onto the reflector, variations of gaps between the reflector and the liquid crystal are brought about, thus causing a poor color tone.
Although removal of the insulating substance attached onto the reflector by etching is also conceived, the surface of the reflector is corroded during etching of the insulating substance, and hence a reflection efficiency of the light is lowered.
The object of the present invention is to provide a reflection type liquid crystal display device which has a good display quality, a module for use in the reflection type liquid crystal display device and a method of manufacturing the same by burying an insulating substance in gaps between its reflectors and flattening a surface of its semiconductor chip module.
The module for use in the reflection type liquid crystal display device of the present invention comprises a plurality of switching elements formed on a semiconductor substrate, a first insulating film formed on the semiconductor substrate, a plurality of reflectors formed on the insulating film, each of which is electrically connected to corresponding one of switching elements via corresponding one of connecting plugs buried in the insulating film, and a second insulating film buried in a gap between the reflectors, the second insulating film securing flatness of a surface of the reflector.
In the present invention, the second insulating film is buried in the gap between the reflectors, and the second insulating film secures the flatness of the surface of the module. With such structure, a good display characteristic can be obtained.
A method of manufacturing the module for use in the reflection type liquid crystal display device of the present invention comprises: a switching elements formation step for forming a plurality of switching elements on a semiconductor substrate; a first insulating film formation step for forming a first insulating film on the semiconductor substrate; a connecting plug formation step for forming a connecting plug buried in the first insulating film so as to be connected to the switching element; a reflector formation step for forming a plurality of reflectors electrically connected to the respective switching elements via the connecting plug; a second insulating film formation step for forming a second insulating film on the semiconductor substrate, the second insulating film burying gaps between the reflectors; and a chemical mechanical polishing step for chemical mechanical polishing the second insulating film.
In the present invention, after the reflectors are formed, the second insulating film is buried in the gaps between the reflectors. Then, the surface of the second insulating film is flattened by a CMP (Chemical Mechanical Polishing). Thus, gaps between the reflectors and liquid crystals are made to be uniform, and a good display characteristic can be obtained.
In this case, when a cover film made of silicon nitride (SiN) or silicon oxynitride (SiON) is formed on the reflector, and the second insulating film is subjected to the CMP using the cover film as a stopper, it is possible to prevent the reflector from being polished. When the second insulating film is made of SOG or HDP (High Density Plasma), the second insulating film can be used as a stopper during the CMP because SiN and SiON shows a higher hardness than that of this insulating film. Moreover, oxidation of the reflector is prevented by this cover film, and a good reflection characteristic can be maintained for a long period of time.
Also when the cover film is made of titanium nitride (TiN) or titanium (Ti), the cover film can be used as a stopper during the CHP. Note that since the transparency of the cover film is low, the cover film must be removed after the CHP in this case.